ANNUAL CLIMATOLOGICAL SUMMARY
FT. SNELLING MN
The 1843 Ft. Snelling climatological record consists of: four daily fixed time readings taken from the station's "detached" thermometer; daily precipitation values; four daily fixed time sky cover observations; four daily fixed time observations of wind "force" and wind direction; two daily fixed time wet bulb readings (taken during the warmer portions of the year only): and several miscellaneous data items. Beginning on 11 January 1843 , temperature, sky cover and wind direction/force observations were taken at or about local sunrise, at or about 0900 hours, at or about 1500 hours and at or about 2100 hours local solar time. Wet bulb readings were taken at local sunrise and at 1500 hours local time. Although extant records give no indication of the time at which 1843 precipitation observations were taken, contextual evidence suggests either a 2100-2100 schedule and/or an early morning (probably "sunrise") schedule (which, in at least in some instances, involved the concomitant "shifting" of precipitation values from the date on which the observation was actually made to the day immediately preceding).
The 1843 Ft. Snelling temperature record is from a thermometer(s) supplied by the U.S. Army Surgeon General as part of an overall restructuring of the military's meteorological network. The instrument(s) involved was purchased from George Tagliabue, New York City, a highly regarded manufacturer of scientific equipment. In addition to providing military installations with new -- and presumably more accurate and reliable -- thermometers, 1843's "modernization" program included adoption of: a) the aforementioned sunrise/0900/1500/2100 hour observation schedule; and b) an expanded and quantified (but non-instrumental) method of taking wind and sky cover observations. Wind velocities were recorded at each of the station's four daily observations, using a standardized/quantified wind force value selected by the observer after noting the effect of the wind on flags, trees, signs and other easily movable objects . The amount of cloudiness was similarly quantified, using a scale of zero (complete overcast) to ten (a totally cloudless sky) .
Comparison of sunrise, 0900 and 1500 hour readings taken by fort observers during the summer months of 1843 indicate that the new thermometer(s) was poorly placed: although the new instructions clearly indicated that thermometers were to be exposed to the north and in a fully shaded area, many 0900 hour readings taken during the summer months approach or exceed readings taken at 1500 hours, suggesting, obviously, that the station thermometer was exposed to the direct rays of the mid-morning sun.
Extant evidence suggests that 1843 Ft. Snelling precipitation records are, on balance, more complete and reliable than their earlier counterparts. When compared with modern records they do, nevertheless, appear to significantly understate the number of days on which precipitation occurred. This suggests that the Fort's 1843 observers -- following the example of their predecessors -- did not routinely/consistently measure and/or record small amounts of precipitation, ignoring small rainfall or snowfall events (possibly by discarding small "catches" or by allowing small amounts of precipitation to evaporate in the gauge and/or to accumulate for inclusion in subsequent "significant" precipitation measurements).
Although the 1843 Fort Snelling record includes daily liquid/melted precipitation values and a record of the TYPE of precipitation observed, it includes NO QUANTITATIVE snowfall values (whether of fresh snowfall or accumulated snow cover). Any snowfall values contained in the foregoing compilation, therefore, are estimates obtained by applying the National Weather Service meltwater-snowfall conversion matrix to the meltwater values recorded by Ft. Snelling observers on 1843 "snow days".
In addition to outdoor temperature, sky cover, precipitation and air movement data, the 1843 Ft. Snelling record includes four daily entries in the barometric and "attached" thermometric portions of the station's Meteorological Register (S.G. form 3). Curiously, however, entries in the barometric columns consist, not of atmospheric pressure values, but of temperature values probably taken from the indoor thermometer attached to the station barometer. Entries in the "attached thermometer" columns of the station's meteorological registers are even more incongruous, seemingly unrelated to any actual air temperature value (whether indoor, outdoor, dry or wet bulb, etc.). So far as can be determined, they are, rather, a probable record of the adjustment factors used to correct barometric readings for the effects of temperature on the station's mercury barometer . Unfortunately, however, any barometric readings taken in 1843 were either never recorded or, if recorded, were included in a now lost or discarded set of records.
The foregoing 1843 temperature record includes both unadjusted (UNADJ) and adjusted (ADJ) mean temperatures. Unadjusted values are the averages of the four fixed time readings taken daily during 1843 . Adjusted averages are from Charles J. Fisk's 1984 "Reconstruction of Daily 1820-1872 Minneapolis -St. Paul Temperature Observations". These values were obtained by averaging statistically derived estimates of the daily maxima and minima that would have been recorded had the Ft. Snelling station been equipped with self-registering thermometers read and re-set at midnight . The foregoing 1843 record also includes both the monthly and annual extreme temperatures (highest daily minimum, lowest minimum, etc.) estimated by Fisk and the monthly extremes actually recorded/observed (OBSRV) by fort observers. All 1843 temperature distributions (e.g. days 90 F or higher, 32 F or lower, etc.) are based on Fisk's estimates of daily maxima and minima.
All foregoing monthly mean cloudiness and monthly mean force of wind values are the simple average of the numeric "clearness" and "force of wind" values derived from the station's four daily visual observations of sky cover and air movement. The foregoing monthly prevailing wind values are derived from daily entries indicating the direction of the wind at sunrise/0900/1500/2100: prevailing winds are those most frequently observed/recorded during any given month.
Estimated maximum and minimum temperature values for the period, 1-10 January 1843, are statistically derived estimates derived from fixed time readings taken on those dates at Ft. Crawford WI (Prairie du Chien). Extant evidence suggests that the precipitation record for the months of February, March, April, June, July, August, October and November 1843 may be incomplete: remarks entered in the station's 1843 meteorological registers indicate that observers failed to measure and/or record small amounts of precipitation which fell on one or more days during those months.
Cold early January. Warm late January. Force eight winds and heavy snow on 27 January. Snowy, stormy and very cold February: sunrise readings of -22 F, -23 F, -20 F, -23 F and -20 F on 6, 7, 16, 17, 28 February, respectively. "Violent" snowstorm on 25-26 February: force five winds recorded on 26 February. Record cold March: sunrise readings of -16 F, -20 F, -16 F, -17 F, -20 F, -18 F, -15 F, -15 F and -11 F recorded on 1, 2, 3, 8, 13, 16, 23, 26, 30 March, respectively. Afternoon readings of 20 F or below each day, 19-26 March. No temperatures, 32 F or higher, recorded at any time during March. Force seven winds on 14, 20 March; force eight winds on 27 March. So far as can be determined, no excessive snowfalls occurred during March. Very cold and windy (force eight winds) on 1 April: probable overnight minimum of zero F or lower. Rapid early April warm-up: 1500 hour reading of 62 F on 12 April. Force seven winds on 25, 27, 30 April. Cool May: sunrise readings of 27 F and 33 F on 1, 16 May, respectively. Mixed rain and snow on 5 May. Lake Pepin not clear of ice until 20 May 1843. Cool, cloudy June: afternoon readings of 56 F, 58 F, 54 F, 56 F and 54 F on 2, 3, 4, 5, 8 June, respectively. Warm and humid late June with heavy rains on 27 June. Thunderstorm with "high" winds on 1 July. Many days with hazy conditions noted during July. Cool August. Haze and/or fog noted on many days during the month. Force eight winds on 23 August. Wet, cloudy September. Sunrise reading of 38 F on 10 September. Force eight winds on 20, 22 September; force seven winds on 17 September. Afternoon readings of 48 F on 25, 27 September. Very cold October: sunrise readings of 22 F, 20 F, 11 F and 10 F on 13, 28, 29, 30 October, respectively. Afternoon readings of 36 F, 35 F, 36 F, 34 F, 29 F, 28 F, 23 F, 25 F and 27 F on 7, 14, 16, 21, 25, 27, 28, 29, 30 October, respectively. Force seven winds on 4, 5 October. Cold, cloudy November. Force eight winds on 8 November. Warm, cloudy December. Heavy rain on 31 December, continuing into 1-2 January 1844 (1.03 inches recorded).